I'm laughing at you people who are saying that Apple is a tiny little company that UPS could give a damn about. You seem to forget that Apple is the customer in this scenario. When they gave UPS a massive amount of money to ship out their products, that money most likely came with a contract, and somewhere in that contract there is verbage about release dates.
There is precedence for this to. Books, games, movies, etc. It's not the first time and won't be the last time something sits in a shipper's warehouse for a few days before it goes to its intended destination.